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B_COND was a straight contradiction of the rule the rest of the enum follows.
No assembler has a mnemonic called `b.cond`; it has `b.eq`, `b.le`, `b.ne` and
thirteen more, and x86 in this same library already models exactly this shape
the right way -- JE, JNE, JG, JLE are sixteen separate mnemonics with the
condition in the opcode.
Two things were wrong with folding it into an operand.
The condition is not an operand. It is four bits of the opcode, no different
from x86 putting Jcc's condition in the low nibble of 0x7_. Modelling it as
one has to be papered over everywhere: the printer special-cased B_COND to
rebuild `b.eq` out of operand 0, sbprint had to skip that operand so it did
not print twice, and the public mnemonic_to_string -- which has no instruction
to read the operand from -- returned "b_cond", a string no assembler takes.
All three of those are now gone; the name prints itself.
More importantly it destroyed the flag data. x86 records per condition which
status bits it consults: JE reads {ZF}, JLE reads {ZF, SF, OF}. One B_COND
entry could not say that, so it claimed nzcv_rd = {N, Z, C, V} -- all four
flags, for every condition. Every entry was wrong. Split apart they carry what
they actually read:
b.eq/b.ne Z b.hi/b.ls Z, C
b.cs/b.cc C b.ge/b.lt N, V
b.mi/b.pl N b.gt/b.le N, Z, V
b.vs/b.vc V b.al/b.nv none
which is the data the compiler's asm checker reads for flag liveness, now that
arm64 feeds it.
The mask also covers the condition field for the first time (0xFF000010 ->
0xFF00001F): with the condition in an operand, four opcode bits sat outside
the mask.
BC.cond gets the same treatment. Builders come out per condition, so `b.le` is
`inst_b_le(label)` rather than `inst_b_cond(.LE, label)`. Cond stays exactly as
it is -- CSEL, CSINC, CSINV, CSNEG, CCMP, CCMN and FCSEL take a real condition
operand, and the compiler's OP_COND handling is untouched.
All sixteen verified by disassembling our own output with llvm-mc: b.eq, b.ne,
b.hs, b.lo, b.mi, b.pl, b.vs, b.vc, b.hi, b.ls, b.ge, b.lt, b.gt, b.le, b.al,
b.nv. Rows follow the table's current column formatting. All rexcode suites
pass and the generators stay idempotent.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>